1. Technical Field of the Invention
The present invention relates to a plasma processing apparatus utilizing a high-frequency wave.
2. Description of the Related Art
Conventionally, there is known a plasma processing apparatus which includes an antenna consisting of an annular waveguide arranged on the upper face of a processing container to supply its interior with a microwave, as shown in FIG. 17 (Japanese Patent Publication kokai No. 11-121196).
This plasma processing apparatus 11 has a processing container 13 on which an antenna 15 is mounted. The antenna 15 is formed by an annularly-curled waveguide having its end closed and has slots 17 . . . formed on the side of the processing container 13. The other end of the antenna 15 is connected to a microwave oscillator 19.
In the plasma processing apparatus 11, the microwave from the microwave oscillator 19 is reflected on an end 21 of the antenna 15 to form a standing wave in the waveguide. Then, the microwave is emitted into the processing container 13 through the slots 17 . . . thereby to generate a plasma for processing.
While, FIG. 18 shows another plasma processing apparatus 31 (Japanese Patent Publication kokai No. 5-34598) in which an antenna 35 in the form of an annular waveguide is wound around the outer periphery of a processing container 33 and also connected to a microwave oscillator 39 through a waveguide 37. In operation, the microwave supplied from the microwave oscillator 39 is divided into left and right at a connecting part 41 between the waveguide 37 and the antenna 35. Then, the so-divided microwaves meet again at a part 43 on the opposite side of the connecting part 41 and is reflected mutually to form a standing wave in the antenna 35. Through slots 45 . . . formed on the inner side of the antenna 35, the microwaves are emitted into the inside processing container 33, so that the plasma is produced in the processing container 33 for processing.
Further, FIG. 19 shows a plasma processing apparatus 121 (Japanese Patent Publication kokai No. 11-40397) which includes an antenna 125 consisting of an annular waveguide arranged on the upper face of a processing container 123. The antenna 125 has a plurality of slots 127 . . . formed on the side of the processing container 13. The upper face of the annular antenna 125 is connected to a waveguide 129 for supplying a microwave, perpendicularly. A convex ridge 131 is formed at a joint part between the waveguide 129 and the antenna 125. The microwave propagated from the waveguide 129 is divided to two groups of microwaves at the convex ridge 131. Then, the so-divided microwaves meet again on the opposite side of the joint part and is reflected mutually to form a standing wave in the antenna 125. The plasma processing apparatus 121 is adapted so as to emit a microwave from the standing wave toward the processing container 13.
In the above plasma processing apparatuses 11, 31, 121 each forming the standing wave in the antenna, however, the microwave has different intensities at each node and antinode of the standing wave. Thus, due to the positional relationship between node and antinode in the antenna, a problem arises in that the interior of the processing container has an electromagnetic field of uneven intensity. Additionally, if the position of each node of the standing wave is deviated from the slot of the antenna, the uniformity of electromagnetic field cannot be maintained in the processing container, causing a problem of impossibility to produce the plasma uniformly, hitherto.